There are over 2,000 known serovars of Salmonella enterica. These serovars differ dramatically in their host range and pathogenicity. Humans suffer tens of millions of infections and perhaps hundreds of thousands of deaths each year from infection by Salmonella enterica. About 100 serovars in subspecies I are responsible for more than 99 percent of these infections. The Salmonella genome sequences obtained, so far, indicate that serovars differ in the presence or absence of many hundreds of genes and these differences are presumably responsible for some of the differences in host range and pathogenicity. This project will characterize many of the gene differences among unsequenced serovars that are major pathogens of humans and domestic animals. In the previous grant period we placed on a microarray PCR products for almost all of the genes identified, so far, in the sequenced Salmonella. Aim 1: New Salmonella enterica genes will be placed on the array as they become available. Aim 2: The array will be used to probe unsequenced Salmonella enterica subspecies I genomes to determine the distribution of gene homologues among serovars. Aim 3: Sequenced enterobacterial genomes reveal "hotspots" of diversity at certain locations where insertion, deletion or replacement events, involving one or more genes, distinguish genomes from each other. These differences will be characterized in unsequenced genomes by PCR and also by direct genome sequencing, capturing some of the variation not found in the currently sequenced genomes. Aim 4: The consequences of insertion/deletion and rearrangement on the otherwise highly conserved order of the Salmonella genome will be studied. The information gained in these four aims will be a step forward in understanding some of the evolutionary mechanisms behind the phenomenal diversity in host-range and pathogenicity of the Salmonella. This information should also be useful in developing tools for epidemiology and could lead to revisions of Salmonella taxonomy, which is currently largely reliant on phage typing and immunological measurements of surface antigens. As a member of S. enterica subspecies 1 was the only bacteria previously used for a bioterror attack in the USA, prior to the use of Anthrax, such studies take on an added dimension.